Synthesis, Characterizations And Catalytic Properties Of MWW-Type Zeolite And Ti-SU-32 Chiral Zeolite

This dissertation focused on the synthesis,characterizations and catalytic properties of aluminosilicate and MWW-type zeolites using line-type quaterbary ammonium cations as structure-directing agents(SDAs),and also studied a new zeolite with a chiral structure, SU-32.In the first part,we used various linear quaternary ammoniums as SDA to synthesize aluminosilicates.Mordenite was obtained at NaOH/SiO₂ ratio lower than 0.6,and Omega was synthesized at NaOH/SiO₂ ratio above 0.6.When LiOH was added instead of NaOH, no pure zeolite phase but mixed crystalline zeolite products were obtained.The second part is about the synthesis of MWW-type zeolite.Its titanosilicate,well known as Ti-MWW,is shown to be a promising catalyst in the selective oxidation of a variety of organic chemicals with H₂O₂ as an oxidant.Thus,it has been of great interests to develop new synthesis methods for MWW zeolites during the last decade.In my research,a system of commercially available linear quaternary ammoniums, octyltrimethylammonium(OCTMAOH),heptyltrimethylammonium(HEPTMAOH),and hextyltrimethylammonium(HEXTMAOH),were used to direct the formation of MWW-type borosilicate.In order to obtain pure MWWphase,various parameters,such as the amount of SDA,boric acid and different alkali cations,were investigated in detail. Ti-MWW was synthesized successfully using all these three kinds of SDAs from the gel containing greatly reduced boric acid in comparison to conventional synthesis with piperidine or hexamethyleneimine.These linear SDAs were quite different from those already used organic amine in the formation of MWW-types zeolites because of their unique shape and size.So the obtained Ti-MWW had not regular shape as evidenced SEM,and these materials tended to be MCM-56 analogues.The structure of products was also characterized by XRD,FT-IR,¹³C CP/MAS NMR,TGA etc.The results proved that SDA were located in two different channels,occupyed the intralayer sinusoidal 10-MR channels(0.41×0.51 nm) and served as an intercalating agent or spacer to construct the interlayer structure,which was the same case of already known organic SDAs. UV characterization indicated that the Ti species existed as both active tetrahedral in the framework and non-active octahedral Ti on external surface.After acid treatment,the non framework Ti species were removed selectively.The catalytic properties of as-made titanosilicate have been investigated in the epoxidation of 1-hexene with with hydrogen peroxide.Acid treated Ti-MWW showed high intrinsic activity for the epoxidation of 1-hexene.In the third part,since a new kind of zeolite with chiral structure,SU-32,has been reported recently,we have tried to incorporate Ti into its framework to synthesize Ti-SU-32.The ratio of diisopropylamine(DIPA as SDA) to germanium dioxide was much lower than that reported in literature.Ti-SU-32 was then prepared successfully at a greatly reduced anount off DIPA.DIPAs were removed out from the channels without intact to structure after calcination in air at 663 K.The UV-vis spectra of as-synthesized Ti-SU-32 showed two bands around 220 and 260 nm.After acid treatment,the catalytically non-active octahedral Ti species were removed.But the acid treated products were not thermally stable on calcination, which limitted the application of Ti-SU-32 in catalysis.More researches need to be carried out to overcome this problem.